Thieno-imidazole based small molecule hole transport materials for dopant-free, efficient inverted (p–i–n) perovskite solar cells

Abstract

Two dipolar molecules based on a thieno-imidazole core, AI109 and AI112, were developed to study the effect of imparting polarity on the hole transport properties in inverted perovskite solar cells (PSCs). These hole transport materials (HTMs) exhibit comparable optoelectronic properties but distinct film morphology and charge transport characteristics. Besides, the new materials with very low concentrations (1 mg mL⁻¹) are able to form smooth and continuous films. The PSCs based on AI109 and AI112 without any dopants and additional interlayers have achieved increased power conversion efficiencies of 13.32% and 13.42%, respectively, compared to those of the standard HTMs, 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamino)-9,9′-spirobifluorene [Spiro-OMeTAD, (11.62%)] and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate [PEDOT:PSS, (12.01%)]. The excellent hole mobility and the superior film morphology of the AI-HTMs account for their higher efficiencies.